The present invention relates to an image display device; and, more particularly, the invention relates to an image display device which includes display devices having two display screens of different display data quantities and which can perform a display of images on respective display devices alternatively or simultaneously.
With respect to miniaturized equipment, such as a portable information terminal, including a mobile telephone or the like, it is expected that good availability and power saving can be achieved by providing a first screen which displays simple information, such as the indication of time, status information or manipulation information involving the equipment separate from a second screen for displaying main, more useful information, such as communication information, content information and the like. For example, in a standby state of equipment having individual screens on two surfaces of a body thereof, such as a folding type portable telephone, by setting in an operable state only the screen having a small size and low power consumption, because it is used to display only a small display data quantity, and by operating the other screen to display the required display data quantity in transmitting and receiving communication information, low power consumption can be achieved as a whole.
Conventionally, in an image display device of this type having two separate screens, the display devices which constitute the respective screens are operated using individual signal drive circuits. However, in order to incorporate two display devices which are driven independently from each other in a mobile telephone or the like, the inner volume of a limited housing of such a device is restricted, and, at the same time, a circuit which drives the driving circuits provided for the respective devices in response to states of use thereof becomes necessary, and, hence, the circuit constitution becomes complicated and drives up the cost.
To cope with such a situation, it may be possible to realize a miniaturization, reduction of weight and low power consumption in equipment in which the image display device is mounted by adopting a common use of the signal line drive circuit. For example, with respect to the liquid crystal display device described in patent literature 1 (Japanese Unexamined Patent Publication 2001-67049), first and second liquid crystal display panels, which differ in the number of signal lines displayed thereon, are used as two display devices which have different display capacities (number of signal lines), wherein the signal lines of the liquid crystal display panel with a large display capacity are extended to the liquid crystal display panel having the signal lines with a small display capacity to allow the common use of these extended lines, whereby the respective liquid crystal display panels are driven using a common signal line drive circuit.